Specific scent glands and other biological odor sources are now recognized to have important communication functions in many phyla of the animal kingdom, including primates and possibly man. Olfactory stimulation from such natural sources may elicit specific behavioral responses or change the neuroendocrine status of an organism. In addition, normal behavioral responses to these natural odors are often modulated by endogenous hormone levels of both sender and recipient organisms. There are several broad questions to be answered about the mechanisms involved in olfactory communication in mammals, including: 1) How do natural scents activate the olfactory and vomeronasal organs? 2) Are there special modes of activation for behaviorally important odors, like pheromones or are all odorants regardless of origin and import, treated in the same way? 3) Once the system has been activated are there distinctive coding mechanisms which operate in selected anatomical regions for particular classes of odorants? 4) What is the neuroanatomy of the olfactory an vomeronasal systems especially with regard to those areas concerned with the perception of pheromones? 5) What is the importance of olfactory signals in mating and other social behaviour? The hamster will be the primary model system because it has well recognized sources of natural scents, several of which have been analyzed chemically, specific scent marking behaviors for their deposition and easily measured behavioral responses to their perception. In this project gas chromatographic, neuroanatomical, electrophysiological and behavioral techniques will be utilized at appropriate levels of the olfactory and vomeronasal systems to answer the above and related questions about the mechanisms of olfactory communication.